Transcranial magnetic stimulation induction coil device with attachment portion for receiving tracking device

ABSTRACT

A transcranial magnetic stimulation (“TMS”) induction coil device includes an attachment portion for attachment to a tracking device and providing that the tracking device, when attached to the TMS coil device, is at a predetermined location and orientation in relation to a casing of the TMS coil device. The casing of the TMS coil device also includes a reference point for confirming the accuracy of the attachment of the tracking device to the TMS coil device at the predetermined location and orientation in relation to the casing.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/823,966 filed Aug. 30, 2006, assigned to the assignee of thisapplication and incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to transcranial magneticstimulation and, more particularly, attachment of a tracking device to atranscranial magnetic stimulation (“TMS”) induction coil device for usein tracking the location of the TMS coil device in relation to asubject's head.

BACKGROUND OF THE INVENTION

Transcranial magnetic stimulation (“TMS”) uses an induction coil toinduce an electric field (“E-field”) within the brain. The locations ofthe brain exposed to a strong enough E-field will become activated, orstimulated. In navigated brain stimulation (“NBS”), the E-field inducedin the brain by a TMS induction coil device is graphically representedon a display. As part of NBS, a three-dimensional (“3D”) localizationsystem is used to locate the TMS coil device accurately with respect toa subject's head. The localization system correlates TMS coil devicelocation information with anatomical information representative of asubject's brain, which typically is obtained from magnetic resonanceimaging (“MRI”) of the brain. The E-field information is shown as anoverlay on a graphical display of the subject's brain generated from theMRI images of the brain. By viewing the display, the user caninteractively position the TMS coil device, in real time, in relation tothe brain to stimulate a desired location of the brain.

A TMS induction coil device typically includes coils having 5 to 30loops (windings) of copper wire located in a casing. The windings arenormally circularly shaped or in the form of a FIG. 8. The shape, andthe location of the maximum, of the E-field induced in the brain dependon the exact shape of the coil windings within the TMS coil device andtheir location and orientation with respect to the brain. In NBS, thestrength and location of the E-field induced in the brain by the TMScoil device is determined from information representative of thelocation and orientation of the casing of the TMS coil device inrelation to the brain and the location and orientation of the coilwindings within and in relation to, respectively, the casing. Thelocation and orientation of the casing is obtained from a navigation ortracking device, such as an infrared tracking device including aninfrared transceiver and infrared reflective elements attached to theTMS coil device, that tracks the movement of the casing, as isconventional in the art. The location and orientation of the coilwindings within the casing are determined by generating a model of thecoil windings within the casing of the TMS coil device using informationobtained from, for example, X-ray images of the casing of the TMS coildevice.

It is known that, in NBS, navigation accuracy and the accuracy of thedetermination of the E-field induced in the brain are greatly affectedby any inaccuracies associated with the tracking of the location of thecoil windings within the TMS coil device with respect to the brain.Current prior art TMS coil devices, however, do not provide that atracking device, such as, for example, a tracking device including threeinfrared reflective elements positioned at a predetermined orientationand spacing with respect to one another as is conventional in the art,is at a predetermined location and orientation or rotation angle on thecasing of the TMS coil device each time that the tracking device isattached to the TMS coil device, such that the location and orientationof the reflective elements in relation to the casing are fixed.

For example, current TMS coil devices do not include a firm and solidcoupling structure to which a tracking device can be attachedconveniently and with ease, and where the coupling structure wouldsubstantially maintain its shape even after the tracking device has beenrepeatedly attached to and detached from the coupling structure. In theprior art, a tracking device is typically attached to a handle extendingfrom the casing of a TMS coil device. The handle usually is a round,tubular plastic part having a relatively thin wall thickness. Therounded shape of the handle permits the tracking device to rotate easilyabout the handle, should a clamp securing the tracking device to thehandle loosen even slightly. Further, based on the thin wall thicknessof the handle, an originally round handle of a TMS coil device has beenknown to flatten slightly after repeated attachment and detachment ofthe tracking device.

Thus, the construction and configuration of handles of prior art TMScoil devices which the tracking device is attached to and detached fromdo not provide that the tracking device can be repeatedly attached tothe TMS coil device at the same location and orientation in relation tothe casing of the TMS coil device, and consequently to the coil windingsin the casing. Each time that a tracking device is attached to a handleof a prior art TMS coil device, or sometimes following prolonged use ofthe TMS coil device with the tracking device attached thereto, acalibration must be performed to determine the location and orientationof the reflective elements of the tracking device in relation to thecasing, and thus to the coil windings contained in the casing. The needfor repeated calibaration of the tracking device is undesirable.Furthermore, the possibility that the tracking device does not remaincalibrated with respect to the casing, following an initial calibrationwhen the tracking device is attached, can cause inaccuracies in therepresentation of the position and orientation of the casing in relationto the brain, and thus inaccuracies in the position of the E-fieldinduced on the brain represented on a display as part of NBS performedwith the TMS coil device, which are not known to the user during use ofthe TMS coil device.

Further, prior art TMS coil devices are ordinarily sold without anyaccompanying information that identifies locations on the casing of theTMS coil device which constitute fixed points of reference that can beused in connection with information obtained from a tracking deviceattached to the TMS coil device to accurately track movement of the TMS7device in relation to the subject's head.

Therefore, there exists a need for a TMS coil device having anattachment portion which a tracking device can be repeatedly attached toand detached from with relative ease, and where, when the trackingdevice is attached to the attachment portion of the TMS coil device, thetracking device is at substantially the same, predetermined location andorientation in relation to the casing, and consequently the coilwindings in the casing.

SUMMARY OF THE INVENTION

In accordance with the present invention, a TMS coil device includes atracking device attachment portion having a configuration and sizecomplementary to, and providing for precision mating and fixedattachment with, a mating attachment portion of a tracking device. Eachtime that the mating portion of the tracking device is fixedly mated tothe tracking attachment portion of the TMS coil device, so as to attachthe tracking device to the TMS coil device, the tracking device is at apredetermined location and orientation in relation to a casing of theTMS coil device.

In one embodiment of the invention, the casing of a TMS coil deviceincludes the attachment portion, and the attachment portion and themating portion are constructed to remain substantially structurallyunchanged following repeated attachment of the tracking device to, andremoval of the tracking device from, the TMS coil device.

In a further embodiment of the invention, the TMS coil device includingthe attachment portion has reflective material covering at least onelocation on an outer surface of the TMS coil device. The locationdefines a reference point that can be used to check the accuracy withwhich the tracking device is attached to the TMS coil device at anexpected, predetermined location and orientation in relation to the TMScoil device. In one embodiment, an actual reference coordinate frame forthe TMS coil device is generated based on the detected location of thereference point in relation to the detected location of a plurality ofreflective elements of the tracking device attached to the TMS coildevice, and the actual reference coordinate frame is compared to anexpected, reference coordinate frame for the attached tracking device inrelation to the TMS coil device. Based on any variance between theactual and expected reference coordinate frames, tracking deviceattachment calibration data for the TMS coil device with the attachedtracking device, which is for use in performing NBS and based on theexpected, reference coordinate frame, is suitably adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will be apparentfrom the following detailed description of the presently preferredembodiments, which description should be considered in conjunction withthe accompanying drawings in which like references indicate similarelements and in which:

FIG. 1 is a side, perspective view of an exemplary TMS coil deviceincluding an attachment portion to which a mating portion of a trackingdevice can be coupled in accordance with the present invention.

FIG. 2 is a cross-sectional view of a portion of the casing of the TMScoil device of FIG. 1 taken along line 2-2.

FIG. 3 is a cross-sectional view of the casing of the TMS coil device ofFIG. 1 taken along line 3-3.

FIG. 4 is a bottom, perspective view of the TMS coil device of FIG. 1with the tracking device attached to the TMS coil device, in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention of providing for precise attachment of a TMS coildevice to a tracking device, such that the tracking device is at apredetermined position and orientation in relation to a casing of theTMS coil device containing coil windings each time that the trackingdevice is fixedly attached to the TMS coil device, is illustrated belowin connection with a TMS coil device having a casing defining a recessfor receiving and precisely mating with a complementarily configuredmating attachment projection of a tracking device. It is to beunderstood, however, that any suitable coupling means known in the artfor mating a first device with a second device, at precisely the samelocation and orientation in relation to the second device each time thatthe first device is fixedly mated to the second device, can be used inconnection with the TMS coil device and the tracking device,respectively, so long as the coupling means are compatible for use inperforming transcranial magnetic stimulation using the TMS coil deviceand the tracking device of interest.

FIG. 1 shows an exemplary embodiment of a TMS coil device 10 including atracking device attachment portion 12, in accordance with the presentinvention, to which a tracking device can be repeatedly, preciselyfixedly attached and then removed, and where each time that the trackingdevice is fixedly attached to the attachment portion 12, the trackingdevice 20 is at a predetermined location and orientation in relation tothe device 10, and in particular coil windings (not shown) contained ina casing 14 of the TMS coil device 10. Referring to FIG. 1, the casing14 of the TMS coil device 10 includes a bottom portion 16, whichcontains the coil windings, and the attachment portion 12. Theattachment portion 12 extends vertically away from a top outer surface24 of the bottom portion 16 and connects to a handle 17 of the TMS coildevice 10. In a preferred embodiment, the coil windings have apredetermined size and shape and are positioned at a predeterminedlocation within and orientation in relation to each other and the bottomportion 16, which also has a predetermined size and shape, as describedin detail in TRANSCRANIAL MAGNETIC STIMULATION INDUCTION COIL DEVICE ANDMETHOD OF MANUFACTURE, U.S. patent application Ser. No. 11/847,511,filed Aug. 30, 2007, assigned to the assignee of this application andincorporated by reference herein (“TMS Coil Device Manufacture patentapplication”). The attachment portion 12 has a predetermined shape andsize complementarily to the size and shape of a mating portion 18 of atracking device 20. The tracking device 20 includes a plurality ofinfrared reflective elements 22 positioned at fixed, predeterminedlocations and orientations in relation to one another, as isconventional and well known in the art. The mating portion 18, which ispreferably made of plastic material, when mated and then securely fixedto the attachment portion 12, attaches the tracking device 20 to the TMScoil device 10 in a precise and predetermined manner.

FIG. 2 shows a cross-sectional view of the casing 14 of the TMS coildevice 10 taken along line 2-2 in FIG. 1. Referring to FIGS. 1 and 2,the attachment portion 12 defines two identical receiving regions 12Aand 12B disposed symmetrically about vertical center line VCL in thecasing 14. Also referring to FIG. 3, which is a view of the casing 14taken along line 3-3 in FIG. 1, the receiving regions 12A, 12B aredisposed symmetrically about horizontal center line HCL in the casing14. Referring to FIGS. 1, 2 and 3, the attachment portion 12 includes atop surface 28 and lateral surfaces 26A, 26B extending between the topouter surface 24 of the bottom portion 16 and the top surface 28, anarcuate surface 31A extending between the center line HCL and thesurface 26A and an arcuate surface 31 B extending between the centerline HCL and the surface 26B. The casing 14 includes a circumferentialsurface 33 a radial distance R1 from a center C of the attachmentportion 12 and a tapered surface 35 extending between the surface 33 andthe handle 17. The circumferential surface 33 circumscribes the topsurface 28.

Referring to FIG. 3, each of the arcuate surfaces 31A, 31B of theattachment portion 12 is a radial distance R2 from the center C, whereR2 is less than R1 and the difference between R1 and R2 is about 10 mm.In addition, each of the walls 26A, 26B is a radial distance R3 from thecenter C, where R3 is less than R2.

The region 12A is defined by the arcuate surface 31A, the lateralsurface 26A, the portion of the surface 28 extending away from thesurface 26A and extending radially away from the surface 31A, and theportion of the surface 24 opposing the portion of the surface 28extending away from the surface 26A and extending radially away from thesurface 31A. The region 12B is defined by the arcuate surface 31B, thelateral surface 26B, the portion of the surface 28 extending away fromthe surface 26B and extending radially away from the surface 31 B, andthe portion of the surface 24 opposing the portion of the surface 28extending away from the surface 26B and extending radially away from thesurface 31 B. The surface 28 includes substantially rectangularly shapednotches 30A, 30B defined by a portion of the surfaces 26A, 26B,respectively, having a height H and a portion of the surface 28 having amaximum width W. The distance between the surface 28 within the notches30 and the opposing surface 24 is H2. The outer surface 33 defines oneend of the notches 30 and a wall surface 38 extending a distance H awayfrom the surface 28 toward the surface 24 defines the other end of thenotches 30. Circumferential surface portion 32 of the surface 33 definesthe maximum width W of the notch portion 30. The notches 30 extend amaximum length L between the wall 38 and the opposing end at the outersurface 33. In addition, referring to FIG. 3, an aperture 41 shown inphantom is defined in the surfaces 31A, 31B symmetrically about the HCLline center and approximately intermediate the surfaces 28 and 24.

Referring to FIG. 1, the mating portion 18 of the tracking device 20 hasa shape and size complementary to the shape and size of the regions 12A,12B defined by the attachment portion 12. The mating portion 18 includesrails 40A and 40B having the same shape and spacing from each other asthe notches 30A, 30B. Further, the mating portion 18 includes an arcuateportion 47 complementary to the arcuate surfaces 31A, 31B and definingan aperture 49. The aperture 49 extends through the arcuate portion 47and is positioned on the mating portion 18 so that the aperture 49 wouldbe aligned with the aperture 41 when the mating portion 18 is matinglyreceived within the receiving regions 12A, 12B of the attachment portion12.

In order to attach the tracking device 20 to the TMS coil device 10, theattachment portion 18 is moved toward and aligned with the matingportion 18 of the tracking device 20, such that the rails 40A, 40B arealigned with the notches 30A, 30B. The rails 40A, 40B are then insertedinto and slid along the notches 30A, 30B until ends 45A, 45B of therails 40A, 40B abut against the wall surface 38 of the notches 30A, 30B,respectively. After the rails 40A, 40B are completely inserted into thenotches 30A, 30B, the attachment portion 12 is precisely mated with themating portion 18 and a screw (not shown) is threaded through theaperture 49 and then the aperture 41 to fix the attachment portion 12 ina mated condition with the mating portion 18. When the attachment andmating portion 12, 18 are in the mated condition, the tracking device20, including the elements 22, are at a predetermined location andorientation in relation to the bottom portion 16 of the casing 14 and,in particular, the coil windings contained in the casing 14.

In a preferred embodiment, precision mating of the tracking device 20 tothe TMS coil device 10, in other words, the tracking device 20 is at apredetermined location and orientation in relation to the casing 14, isachieved without the need of external tools. For example, the portions12 and 18, once mated to each other, do not move relative to each otherbased on friction. Alternatively, the apertures 41 and 49 include, forexample, magnets of opposite polarity that fixedly secure the attachmentportion 12 to the mating portion 18. The magnets are of sufficientstrength to maintain the portions 12 and 18 mated to each other underordinary use of the TMS coil device 10, while also allowing the user toremove the tracking device 20 from the TMS coil 10 when desired bypulling the tracking device 20 away from the TMS coil 10. In a furtherembodiment, a hand operated C-clamp (not shown) can be applied aroundthe portions 18 and 20 when in the mating condition, so as to fixedlysecure the portions 18 and 20 to each other.

In a preferred embodiment, the geometrically complementaryconfigurations of the attachment portion 12 and the matching portion 18advantageously provide that the actual location of the tracking device20 in relation to the casing 14 is typically at most no more than about3 mm, preferably no more than about 1 mm, away from the expectedlocation of the tracking device 20 in relation to the casing 14. In afurther preferred embodiment, the portions 12 and 18 are constructedfrom materials, such as, for example, plastic, that do not readily wearaway when repeatedly rubbed against each other.

It is to be understood that the precision mating of the casing 14 of theTMS coil device 10 to the tracking device 20 illustrated in FIGS. 1-3 isexemplary, and that any suitable structure for coupling the trackingdevice 20 to the casing 14 available in the art, such as, for example,snap-on and resilient coupling components, for establishing a precisionmating between the tracking device 20 and the TMS coil 10, may beimplemented to provide that the tracking device 20 is readily fixedlyattachable to and detachable from the casing 14, and when the trackingdevice 20 is attached and fixed to the casing 14, the tracking device 20is in a predetermined location and orientation in relation to the casing14.

Thus, during use of the tracking device 20 in conjunction with the TMScoil device 10, and also for maintenance, the tracking device 20 iseasily detached from and attached to the casing 14, by uncoupling andcoupling the mating portion 16 from and to the attachment portion 14,respectively, without affecting the location and orientation of thetracking device 20 in relation to the casing 14 when the tracking device20 is attached to the attachment portion 12. As a result, the locationand orientation of the tracking device 20 with respect to coil windings(not shown) contained within the bottom portion 16 of the casing 14 isthe same each time that the tracking device 20 is attached to the TMScoil device 10. Consequently, where the location and orientation of thecoil windings within a casing of a TMS coil device is known in advance,such as where the coil windings are in a casing of the type described inthe “TMS Coil Device Manufacture patent application”, the location andorientation of the coil windings within the casing in relation to thetracking device 20 that can be attached to the TMS coil device 10 alsois accurately known in advance and, therefore, can be used to performNBS without performing a calibration of the tracking device 20 each timethat the tracking device 20 is attached to the TMS coil device 10, or atsome interval following continued use of the TMS coil device 10 with theattached tracking device 20.

Advantageously, the construction of the attachment portion and matingportion provide that the location and orientation of the tracking deviceattached to the TMS coil device with respect to the coil windings in thecasing of the TMS coil device remains unchanged during repeatedattachment and removal of the tracking device to and from the TMS coildevice. Thus, tracking device location and orientation information, onceinitially determined at the manufacturer or in an initial calibration,can be relied upon for future uses of the TMS coil device with thetracking device attached thereto. The invariability of the location andorientation of the attachment portion in relation to the coil windings,thus, provides for improved accuracy when the TMS coil device is used toperform NBS.

FIG. 4 shows a perspective, bottom view of the TMS coil device 10 withthe tracking device 20 attached in a predetermined location andorientation in relation to the casing 14. Referring to FIG. 4, thebottom portion 16 of the casing 14 includes a bottom surface 60 which,during operation of the TMS coil device 10, is placed adjacent or incontact with a subject's head. In accordance with the present invention,the bottom surface 60 includes reflective material at one or morepredetermined locations, for example, at a reference point R1 located atthe center of the bottom surface 60. It is to be understood that areference point also may be included elsewhere on the outer surface ofthe casing 14, or on the outer surface of other portions of the TMS coildevice 10.

Based on information representative of the location of the referencepoint(s) on the casing 14, the accuracy of the location and orientationof the tracking device 20 in relation to the casing 14, when thetracking device 20 is attached to the TMS coil device, can bedetermined, for example, during production of the TMS coil device or inthe field. Information representative of the location of the referencepoint(s) on the casing 14 may be provided with the TMS coil device, forexample, with the sales literature accompanying the TMS coil device. Thesame, conventional tracking system used to detect the position of thereflective elements 22 of the tracking device 20, when attached to theTMS coil device 10, also detects the position of the reference point.The accuracy of the attachment of the tracking device 20 to the TMS coildevice 10, in other words, the difference between the expected andactual location and orientation of the tracking device 20 in relation tothe TMS coil device 10, is determined by using the reference points, forexample, to create a frame of reference. Referring to FIG. 4, thetracking device 20 preferably includes sets of three points P1-P3 orP4-P6, which correspond to sets of three reflective elements 22 and areused to form a reference coordinate frame for the TMS coil device 10,for example, where the origin is at the point R1 and the coordinate axesare as shown in FIG. 4. Standard measurement techniques and softwaretools, as well known in the art, can be used to determine the coordinateframes necessary to check the accuracy of the placement of the trackingdevice 20 in relation to the TMS coil device 10 using the referencepoints and, thus, provide that the TMS coil device 10, in combinationwith the attached tracking device 20, can be used to perform NBS with adesired level of accuracy.

In one embodiment, the expected location and orientation of the trackingdevice 20 in relation to the coil windings in the casing 14, which isknown from the manufacturer of the device 20, is compared to the actuallocation and orientation of the tracking device 20 in relation to thecoil windings in the casing 14, which is determined by a conventionalinfrared tracking system that detects the locations of the referencepoint and the reference elements 22. The actual and expected locationsand orientations are then compared, for example, within a processor of aNBS system, and tracking device calibration data for the TMS coil device10 with the attached tracking device 20, which is used to performnavigated brain stimulation with the TMS coil device 10 and is based onthe expected location and orientation of the tracking device 20 inrelation to the casing 14, is suitably adjusted if a variance existsbetween the expected and the actual locations and orientations.

Although preferred embodiments of the present invention have beendescribed and illustrated, it will be apparent to those skilled in theart that various modifications may be made without departing from theprinciples of the invention.

1. A method for determining the location and orientation of a trackingdevice in relation to a transcranial magnetic stimulation (“TMS”)induction coil device when the tracking device is attached to the TMScoil device for performing navigated brain stimulation, the methodcomprising: providing a TMS coil device comprising: a casing comprisingat least one coil winding and an attachment portion having apredetermined size and shape for removable attachment of the casing anda mating portion of a tracking device, wherein the mating portion has apredetermined size and shape complementary to the predetermined size andshape of the attachment portion, and wherein, when the attachmentportion of the casing and mating portion of the tracking device areremovably attached and configured, such that, during use, the casing andthe tracking device are mated together and are together freely movableby a user with at least one set of two or more reflective elements ofthe tracking device in a fixed location with respect to the casing orthe at least one coil winding of the casing; at least one referencedesignation point defined at a predetermined location on the TMS coildevice and a predetermined distance away from a point defined on theattachment portion; and wherein the tracking device includes the atleast one set of two or more reflective elements at a predeterminedlocation and orientation in relation to each other, and wherein, whenthe tracking device is removably attached to the attachment portion, thetwo or more elements are at a predetermined location and orientation inrelation to the attachment portion; detecting the locations of thereference point and two or more reflective elements of the trackingdevice; generating an actual reference coordinate frame for the TMS coildevice based on the detected locations of the reference point and thetwo or more elements of the tracking device, computing an actuallocation and orientation of the tracking device in relation to the coilwindings in the casing based on the actual reference coordinate frame;and adjusting tracking device calibration data used to perform navigatedbrain stimulation with the TMS coil device including the attachedtracking device if a variance exists between an expected and the actuallocation and orientation of the tracking device in relation to the coilwindings, wherein the calibration data is a based on the expectedlocation and orientation of the attached tracking device in relation tothe coil windings.
 2. The method of claim 1, further comprising the stepof: adapting the TMS coil device to be movable from a first position toa second position with respect to a head of a patient when performingnavigated brain stimulation.
 3. The method of claim 1, wherein the atleast one reference designation point is located on the casing.
 4. Themethod of claim 3, wherein the at least one reference designation pointis located on the bottom surface of the casing.
 5. The method of claim1, wherein at least one of the reference designation points hasreflective material.
 6. The method of claim 5, wherein detecting thelocations of the at least one reference point having reflective materialand two or more reflective elements of the tracking device isaccomplished using the same tracking system.
 7. The method of claim 6,wherein the tracking system is an infrared tracking system.
 8. Themethod of claim 6, wherein the tracking device includes a set comprisingat least three elements at predetermined locations and in predeterminedorientations with respect to each other such that, when the trackingdevice is removably fixed to the attachment portion, the set comprisingat least three elements is at a predetermined location and orientationin relation to the attachment portion and form a reference coordinateframe with the reflective reference point.